Essential fatty acid (EFA) deficiency increases secretion of plasma triglycerides (TG) in rats fed diets wtih sucrose, glucose or fructorse as the carbohydrate for 8-10 weeks. However, even brief EFA depletion will significantly affect liver lipid metabolism, e.g., only one week of depletion will increase activities of liver lipogenic enzymes and levels of cholesteryl esters in liver. Such early changes could be either causes or effects of increased plasma triglyceride secretion by the liver, which is the major source of plasma triglyceride. The aims of our proposed research include: to investigate how increased plasma TG secretion (monitored by increases in plasma TG after Triton WR1339 injection) is related to these early changes in liver lipid metabolism in EFA depletion and to compare effectiveness of various polyunsaturated fatty acids in remedying these changes. We will test also how bile composition and secretion are affected in early EFA depletion, because recent evidence indicates a coordinate regulation between bile acid synthesis and formation of very-low-density lipoproteins (rich in TG). These experiments should provide biochemical evidence on how dietary essential fatty acids modulate this coordinate regulation and its relationship to removeal of triglyceride and cholesterol from the liver. We plan also to continue our studies on interactions of synthetic phospholipids with sterols in simplified systems, to provide information on how fatty acid composition of naturally occurring phospholipids can affect their properties in membranes in vivo.